Table 1.

An overview of metabolomics studies of type 2 diabetes.

Metabolite Type	Direction of Association with Type 2 Diabetes	References
Amino acids	BCAAs (Isoleucine, Leucine, Valine) (↑) AAAs (Phenylalanine, Tyrosine) (↑) Alanine (↑) Glutamate (↑) Methionine (↑) Histidine (↑) lysine (↑) Glycine (–) Glutamine (↓) 2-hydroxybutyrate (↑) 2-aminoadipate (↑)	[11,12,13]
Lipids	Lipoproteins HDL-C (↑) Triglyceride (↑) Glycerolipids Triacylglycerol (↑) Triacylglycerol (↑) Ceramides Dihydroceramide (↑) Phospholipids Phosphatidylcholine (↓) Di-acyl-phospholipids (↑) Lysoalkylphosphatidylcholine (↑) Lysophosphatidylcholine (↑) Alkyl-acyl phosphatidylcholines (↓) (lyso)phosphatidylethanolamines (↑)	[14,15] [16,17] [16,18,19,20,21]
Carbohydrates	Sugar monomer Mannose (↑) Treehouse (↑) Glucose (↑) Hexose (↑) Arabinose (↑) Fructose (↑) Glycolipid (↑) Polyol 1,5-anhydroglucitol(↓)	[16] [22]

The table summarizes previous studies which have investigated the association of metabolites with T2D. (↑), positive association (e.g., higher metabolite, higher risk); (–), controversial; (↓), inverse association (e.g., lower metabolite, lower risk) with prediabetes traits or type 2 diabetes.